Hybrid electric vehicle and powertrain

ABSTRACT

A hybrid electric vehicle and powertrain includes an engine and an electric machine connected to each other in a power-split arrangement. The electric machine is operable as a motor or a generator, and is offset from the engine, thereby reducing the overall length of the powertrain. A power transfer arrangement includes a planetary gear set in which the carrier is directly connected to an output shaft of the engine. The electric machine is connected to the planetary gear set through an intermediate gear, thereby facilitating the offset of the electric machine and the engine and facilitating an easy change of gear ratio for the motor/generator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hybrid electric vehicle and apowertrain for such a vehicle.

2. Background Art

With the ever increasing need to produce vehicles that are more fuelefficient, hybrid electric vehicles (HEV's) have provided an improvementin fuel economy over many conventional vehicles that utilize only aninternal combustion engine to drive the vehicle. One of the primaryadvantages of an HEV is that it allows the vehicle to be powered by oneor more electric motors under certain operating conditions. For example,if the speed of the vehicle is relatively moderate, and the battery orother electrical power source is sufficiently charged, the engine may beshut off, and the vehicle powered exclusively by the electric motors. Asoperating conditions change, the engine may be started to provideadditional power, and if needed, operate a generator to charge thebattery.

Various arrangements of internal combustion engines and electricmachines—i.e., generators and motors—have been utilized in HEV's. Forexample, series arrangements, parallel arrangements, and power-splitarrangements provide different ways for the engine and electric machinesto interact to output torque to drive the vehicle. In one example of apower-split arrangement, an engine and an electric machine are bothoperatively connected to a planetary gear set, the output of whichprovides torque to vehicle drive wheels. One or more additional electricmachines can be used to provide additional torque to the drive wheels,charge an energy storage device, such as a battery, provide electricalenergy directly to another electric machine, or some combinationthereof. In the power-split arrangement, power output from the engineflows through the planetary gear set, where a portion of the power isapplied to the electric machine connected to the planetary gear set, andanother portion of the engine power is transferred to the vehicle drivewheels.

In many examples of power-split arrangements, an engine output shaft isconnected to one of the members of a planetary gear set, and an outputshaft from an electric machine is connected to another of the members ofthe planetary gear set. These two torque-producing devices are oftenin-line with each other, such that their respective output shafts liealong the same axis. In some vehicle platforms, it may be desirable toreduce overall powertrain length by having torque-producing devices thatare not in-line with each other.

In addition, it may be desirable to have a power-split configuration foran HEV powertrain that includes an electric machine having an outputshaft that is not directly connected to a member of the planetary gearset. This would add flexibility to the configuration by providing a wayto adjust gear ratios without changing the basic members of thetransmission—e.g., the members of the planetary gear set.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a hybrid electric vehicleand powertrain having a power-split configuration where the engineoutput shaft and the electric machine output shaft are offset from eachother, thereby providing a shorter length to accommodate smallerpackaging requirements.

The invention also provides a hybrid electric vehicle and powertrainthat include one or more electric machines having outputs that areconnected to intermediate and/or idler gears, such that the gear ratiosfor the electric machines can be changed without changing the primarymembers of the planetary gear set.

The invention also provides a hybrid electric vehicle having a pluralityof wheels, and including an engine and a first electric machine, each ofwhich is operable to output mechanical power. The first electric machineis also operable as a generator, and is configured to receive mechanicalpower from the engine and to output electrical power. The engineincludes an output shaft defining a first axis, and the first electricmachine includes an output shaft defining a second axis. The first andsecond axes are not coincident with each other, thereby providing anoffset between the first electric machine and the engine. A powertransfer arrangement cooperates with the engine and the first electricmachine to provide power flow paths between the engine and at least oneof the vehicle wheels, and between the first electric machine and the atleast one vehicle wheel. The power transfer arrangement includes aplanetary gear set having a plurality of members, including a sun gear,a plurality of planet gears, a carrier connecting the planet gears toeach other, and a ring gear connected to the planet gears. One of themembers of the planetary gear set provides an output member for theplanetary gear set. The engine output shaft is directly connected to oneof the members of the planetary gear set such that the mechanical poweroutput from the engine is split between the first electric machine andthe output member of the planetary gear set.

The invention further provides a hybrid electric vehicle as describedabove, and further includes a second electric machine defining a motoraxis, and having an output connected to one of the members of theplanetary gear set, such that the motor axis is coincident with thefirst axis. In such embodiments, the ring gear may provide the outputmember for the planetary gear set, and a planetary gear reductionarrangement can be connected to the output of the second electricmachine and the ring gear. This increases the torque transferred fromthe second electric machine to the ring gear. In some embodiments, theplanetary gear reduction arrangement includes a plurality of piniongears that are connected to each other by a carrier. The carrier can begrounded to allow the pinions to rotate about their own axes withoutorbiting around the second electric machine.

The invention also provides a powertrain for a hybrid electric vehiclethat includes an engine and a first electric machine, each of which isoperable to output mechanical power to drive the vehicle. Embodiments ofthis powertrain can include a second electric machine that is alsooperable to provide torque to drive the vehicle. The first and secondelectric machines can each be connected to the powertrain through one ormore intermediate or idler gears, and one or more intermediate or idlergears can be used on the output side of the powertrain such that thegear ratios of the electric machines can be changed without changing themembers of the planetary gear set.

In one embodiment of the present invention, a hybrid electric vehiclepowertrain includes an engine and two electric machines connectedthrough a planetary gear set. Specifically, the engine is connected tothe carrier of the planetary gear set, while the first electric machineis connected to the sun gear. An output shaft from the engine isdirectly connected to the carrier, while an output shaft of the firstelectric machine is connected to the sun gear through a first mountedgear attached to its output shaft, and a second gear mounted on a shaftdirectly connected to the sun gear. In this way, the engine and firstelectric machine are offset from each other, thereby reducing theoverall length of the powertrain.

The ring gear provides the output for the planetary gear set, whichprovides power flow paths from the first electric machine and the engineto vehicle drive wheels. The vehicle drive wheels are connected to adifferential, which itself is connected to the ring gear through amounted gear on a differential shaft, and an idler gear intermeshingwith the differential mounted gear and the ring gear of the planetarygear set. The second electric machine is also connected to thepowertrain through a mounted gear on its output shaft, and an idler gearintermeshing with its mounted gear and the ring gear from the planetarygear set. The differential shaft and the shaft of the second electricmachine are also offset from each other, thereby further helping toensure a shorter powertrain.

In some embodiments, the second electric machine can be a relativelysmall unit, and in such a case can be connected to the planetary gearset such that it is in-line with the engine. This can be accomplished byconnecting the first electric machine to the planetary gear set asdescribed above, and providing a central opening through the secondelectric machine so that the sun gear shaft passes through it. Theoutput from the second electric machine can be provided to a planetarygear reduction arrangement to increase the torque provided to the ringgear of the planetary gear set. This may be advantageous, since, asdescribed above, the second electric machine may be a relatively smallunit. As with other embodiments, the output from the planetary gear setcan be through the ring gear, which is connected to an idler gearintermeshing with a mounted gear on the differential shaft. Thus,embodiments of the present invention provide a combination offlexibility with regard to changing gear ratios and compact size toaccommodate the smaller packaging requirements of many HEV platforms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a vehicle and powertrain inaccordance with one embodiment of the present invention; and

FIG. 2 shows a schematic representation of a vehicle and powertrain inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a vehicle 10 in accordance with one embodiment of thepresent invention. The vehicle 10 includes a powertrain 12 having threetorque producing devices: an engine 14 and two electric machines 16, 18.In the embodiment shown in FIG. 1, the first electric machine 16 islabeled “Generator” and the second electric machine 18 is labeled“Motor”; however, it is understood that each of the electric machines16, 18 can act as either a motor to produce mechanical power, or as agenerator to produce electric power upon receiving a mechanical powerinput. The engine 14 and the electric machines 16,18 are each connectedto a power transfer arrangement 19 that provides power flow paths fromthese torque-producing devices to an output of the powertrain 12 todrive the vehicle 10.

The engine 14 includes an output shaft 20 that is connected to a carrier22 of a planetary gear set 24, which is part of the power transferarrangement 19. The carrier 22 connects a plurality of planet gears 25to each other. The planetary gear set 24 also includes a ring gear 26,and a sun gear 28. The sun gear 28 is connected to a first input shaft30, which has a first intermediate gear 32 attached thereto. Thegenerator 16 has an output shaft 34, which has attached to it a firstmounted gear 36. The mounted gear 36 cooperates with the intermediategear 32 to provide a power flow path between the generator 16 and theplanetary gear set 24. As shown in FIG. 1, the output shaft 20 of theengine 14 defines a first axis 38, while the output shaft 34 of thegenerator 16 defines a second axis 40. The two axes 38, 40 are notcoincident with each other, which can help to reduce the overall lengthof the powertrain 12.

As shown in FIG. 1, the vehicle 10 includes a pair of drive wheels 42,44. The drive wheels 42, 44 receive power through a differential 46 inthe powertrain 12. The differential 46 includes an input shaft 48 thatis attached to a second mounted gear 50. The mounted gear 50 intermesheswith a first idler gear 52, which, in turn, intermeshes with a secondintermediate gear 54 mounted to the ring gear 26. The ring gear 26 isthe output member for the planetary gear set 24. Thus, the powertransfer arrangement 19 provides power flow paths from each of thegenerator 16 and the engine 14 through the planetary gear set 24,through the idler gear 52 and the mounted gear 50, and through thedifferential 46 to the vehicle drive wheels 42, 44.

The power transfer arrangement 19 also provides a power flow path fromthe motor 18 to the vehicle drive wheels 42, 44 through the followingelements. The motor 18 includes an output shaft 56 attached to a thirdmounted gear 58. The third mounted gear intermeshes with a second idlergear 60, which itself intermeshes with the gear 54 attached to the ringgear 26 of the planetary gear set 24.

The vehicle 10 and its powertrain 12 provide advantages overconventional power-split arrangements, in that the gear ratios for anyof the torque-producing members can be modified by changing one or moreof the mounted gears 36, 50, 58; one or more of the intermediate gears30, 54; one or more of the idler gears 52, 60; or some combination ofthe above. None of these gear changes, however, requires a change of theprimary elements of the planetary gear set 24. This provides arelatively easy and cost effective way to effect gear ratio changes, forexample, when a power-split configuration is adapted to a new vehicleplatform.

As discussed above, the engine axis 38 and the generator axis 40 areoffset from each other to reduce the overall length of the powertrain12. Similarly, the motor output shaft 56 defines a third axis 62, andthe differential shaft 48 defines a fourth axis 64, which are also notcoincident with each other. This allows the motor 18 and thedifferential 46 to be offset from each other, and again, may help toreduce the overall length of the powertrain 12.

FIG. 2 shows a vehicle 10′ having a powertrain 12′ in accordance withanother embodiment of the present invention. Throughout the descriptionof the vehicle 10′, and the powertrain 12′, elements having counterpartsin the vehicle 10 shown in FIG. 1, are marked with the prime (′) symbol.Similar to powertrain 12, the powertrain 12′ includes an engine 14′having an output shaft 20′ directly connected to a carrier 22′ of aplanetary gear set 24′. The generator 16′ includes an output shaft 34′defining an axis 40′. The axis 40′ is not coincident with axis 38′defined by the engine output shaft 20′. Thus, like the embodiment shownin FIG. 1, the vehicle 10′ provides the advantage of a reduced overalllength for the powertrain 12′ by offsetting the generator 16′ from theengine 14′. Unlike the powertrain 12 shown in FIG. 1, the powertrain 12′includes a second motor 18′ that is directly in-line with the engine14′. The vehicle 10′ provides an example of using a small second motor18′ to reduce the size and weight of the vehicle 10′. Because the motor18′ is relatively small, it can be placed in-line with the engine 14′without undesirably increasing the length of the powertrain 12′.

As shown in FIG. 2, the shaft 30′, which provides an input to the sungear 28′, traverses an opening 65 in the motor 18′ to allow thegenerator 16′ to be connected to the sun gear 28′ with the motor 18′disposed therebetween. Because it is contemplated that the motor 18′will be a smaller electric machine, it may be desirable to increase thetorque output from the motor 18′ to the vehicle wheels 42′, 44′. In theembodiment shown in FIG. 2, this is accomplished through the use of aplanetary gear reduction arrangement 66.

The planetary gear reduction arrangement 66 includes a plurality ofpinions 68 that are connected to each other by a carrier 70. The carrier70 is grounded, which allows the pinions 68 to rotate about their ownaxes without orbiting around the motor 18′. This arrangement providesfor an increase in torque from the motor 18′ to the ring gear 26′, andultimately, to the vehicle drive wheels 42′, 44′. Also shown in FIG. 2,the generator axis 40′ and the differential axis 48′ are coincident witheach other, but can easily be made offset from each other to furtherhelp reduce the overall length of the powertrain 12′. Similar to theembodiment shown in FIG. 1, the gear ratios for the torque producingelements—i.e., the engine 14′, the generator 16′, and the motor 18′—canall be changed without changing the primary elements of the planetarygear set 24′.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. A hybrid electric vehicle having a plurality of wheels, the vehiclecomprising: an engine operable to output mechanical power and includingan engine output shaft defining a first axis; a first electric machineincluding an output shaft defining a second axis that is not coincidentwith the first axis, the first electric machine being operable as amotor to output mechanical power, and operable as a generator configuredto receive mechanical power from the engine and to output electricalpower: and a power transfer arrangement cooperating with the engine andthe first electric machine to provide power flow paths between theengine and at least one of the vehicle wheels, and between the firstelectric machine and the at least one vehicle wheel, the power transferarrangement including a planetary gear set having a plurality ofmembers, including a sun gear, a plurality of planet gears, a carrierconnecting the planet gears to each other, and a ring gear, one of themembers of the planetary gear set providing an output member for theplanetary gear set, the engine output shaft being directly connected toone of the members of the planetary gear set such that the mechanicalpower output from the engine is split between the first electric machineand the output member of the planetary gear set.
 2. The vehicle of claim1, further comprising: a first mounted gear attached to the output shaftof the first electric machine; a first input shaft connected to one ofthe members of the planetary gear set to provide an input member to theplanetary gear set for the first electric machine; and a firstintermediate gear attached to the first input shaft and intermeshingwith the first mounted gear to provide a power flow path between theoutput shaft of the first electric machine and the input member of theplanetary gear set.
 3. The vehicle of claim 2, further comprising: adifferential operatively connected to the at least one vehicle wheel andhaving an input shaft; a second mounted gear attached to the input shaftof the differential; a second intermediate gear attached to the outputmember of the planetary gear set; and a first idler gear intermeshingwith the second mounted gear and the second intermediate gear to providea power transfer path between the output member of the planetary gearset and the at least one vehicle wheel.
 4. The vehicle of claim 3,further comprising: a second electric machine including an output shaft,and operable at least as a motor to output mechanical power; a thirdmounted gear attached to the output shaft of the second electricmachine; and a second idler gear intermeshing with the third mountedgear and the second intermediate gear to provide a power flow pathbetween the second electric machine and the at least one vehicle wheel.5. The vehicle of claim 4, wherein the output shaft of the secondelectric machine defines a third axis, and the input shaft to thedifferential defines a fourth axis that is not coincident with the thirdaxis.
 6. A hybrid electric vehicle having a plurality of wheels, thevehicle comprising: an engine operable to output mechanical power andincluding an engine output shaft defining a first axis; a first electricmachine including an output shaft defining a second axis that is notcoincident with the first axis, the first electric machine beingoperable as a motor to output mechanical power, and operable as agenerator configured to receive mechanical power from the engine and tooutput electrical power: a power transfer arrangement cooperating withthe engine and the first electric machine to provide power flow pathsbetween the engine and at least one of the vehicle wheels, and betweenthe first electric machine and the at least one vehicle wheel, the powertransfer arrangement including a planetary gear set having a pluralityof members, including a sun gear, a plurality of planet gears, a carrierconnecting the planet gears to each other, and a ring gear, one of themembers of the planetary gear set providing an output member for theplanetary gear set, the engine output shaft being directly connected toone of the members of the planetary gear set such that the mechanicalpower output from the engine is split between the first electric machineand the output member of the planetary gear set; and a second electricmachine defining a motor axis and having an output connected to one ofthe members of the planetary gear set such that the motor axis iscoincident with the first axis.
 7. The vehicle of claim 6, wherein thering gear provides the output member for the planetary gear set, and thevehicle further comprises a planetary gear reduction arrangementconnected to the output of the second electric machine and the ringgear, thereby increasing the torque transferred from the second electricmachine to the ring gear.
 8. The vehicle of claim 7, wherein theplanetary gear reduction arrangement includes a plurality of piniongears and a grounded carrier connecting the pinion gears to each other.9. The vehicle of claim 8, further comprising: a first mounted gearattached to the output shaft of the first electric machine; a firstinput shaft connected to one of the members of the planetary gear set toprovide an input member to the planetary gear set for the first electricmachine; and a first intermediate gear attached to the first input shaftand intermeshing with the first mounted gear to provide a power flowpath between the output shaft of the first electric machine and theinput member of the planetary gear set.
 10. The vehicle of claim 9,further comprising: a differential operatively connected to the at leastone vehicle wheel and having an input shaft; a second mounted gearattached to the input shaft of the differential; a second intermediategear attached to the output member of the planetary gear set; and afirst idler gear intermeshing with the second mounted gear and thesecond intermediate gear to provide a power transfer path between theoutput member of the planetary gear set and the at least one vehiclewheel.
 11. The vehicle of claim 10, wherein the input shaft of thedifferential defines an axis that is not coincident with the first axis.12. A powertrain for a hybrid electric vehicle, comprising: an engineoperable to output mechanical power to drive the vehicle and includingan engine output shaft defining a first axis; a first electric machineoperable as a motor to output mechanical power to drive the vehicle andincluding an output shaft defining a second axis that is not coincidentwith the first axis, the first electric machine being further operableas a generator configured to receive mechanical power from the engineand to output electrical power: and a power transfer arrangementcooperating with the engine and the first electric machine to providepower flow paths between the engine and the first electric machine, thepower transfer arrangement including a planetary gear set having aplurality of members, including a sun gear, a plurality of planet gears,a carrier connecting the planet gears to each other, and a ring gear,one of the members of the planetary gear set providing an output memberfor the planetary gear set, the first electric machine being connectedto one of the sun gear or the ring gear, and the engine output shaftbeing directly connected to the carrier, thereby facilitating a transferof at least a portion of the power output from the engine to the firstelectric machine.
 13. The powertrain of claim 12, further comprising: afirst mounted gear attached to the output shaft of the first electricmachine; a first input shaft connected to one of the sun gear or ringgear to provide an input member to the planetary gear set for the firstelectric machine; and a first intermediate gear attached to the firstinput shaft and intermeshing with the first mounted gear to provide apower flow path between the output shaft of the first electric machineand the input member of the planetary gear set.
 14. The powertrain ofclaim 13, the vehicle including a plurality of wheels, the powertrainfurther comprising: a differential having an output operativelyconnected to two of the vehicle wheels and having an input shaft; asecond mounted gear attached to the input shaft of the differential; asecond intermediate gear attached to the output member of the planetarygear set; and a first idler gear intermeshing with the second mountedgear and the second intermediate gear to provide a power transfer pathbetween the output member of the planetary gear set and thedifferential.
 15. The powertrain of claim 14, further comprising: asecond electric machine including an output shaft, and operable at leastas a motor to output mechanical power; a third mounted gear attached tothe output shaft of the second electric machine; and a second idler gearintermeshing with the third mounted gear and the second intermediategear to provide a power flow path between the second electric machineand the differential.
 16. The powertrain of claim 15, wherein the outputshaft of the second electric machine defines a third axis, and the inputshaft to the differential defines a fourth axis that is not coincidentwith the third axis.